Threshold displacement energies

The minimum energy required for displacement is called the displacement threshold energy, 7d, and its mean value (independent of the crystallographic direction) ranges between 20 and 50 eV for all metals. 

As mentioned in Section 2.1, because of the small electron mass, the energy transferred by MeV electrons to nuclei via Rutherford scattering is small and of the order of the displacement threshold energy ( 20eV). Therefore, electron irradiation, performed... 

Minimum displacement threshold energies for Cu atoms in ordered and disordered CujAu and CuAu were determined at 20 K by Alamo et al. (1986) using 0.66 and 2.36 MeV electron irradiations and electrical resistivity measurements. It was found that the minimum displacement threshold energy is l8eV in all... 

In this model, it has been assumed that the incident ions cause a preferential displacement of the graphitic carbon and increase the possibility of sp diamond-like bond formation in the optimal ion energy range. This assumption is based on the values of the displacement threshold of graphite and diamond as 30 eV and 80 eV respectively. Robertson observed that the values are actually much closer to each other, namely, in the range of 25-42 eV for graphite and in the range of 37-45 eV for diamond. 

This formula contains the assumption that energy transfer below the threshold for the displacement of one atom and between the threshold energy for the displacement of one atom and the threshold for the displacement of two atoms takes place via collisions which do not lead to the formation of point defects. 

Since the recoil direction of the stmck atom is determined by the dynamics of the collision, it will be a random variable during real experiments. The directional dependence of Ed, coupled with the randomness of the initial directions of the stmck atom, imply that the notion of a sharp displacement threshold is oversimplified. In reality, there is a range of displacement energies for which a displacement may occur. A weighted average over the displacement directions leads to an average displacement energy, which is the value most typically used as Ed. Typical values of Ed are 16 eV for Si, 29 eV for Cu and 43 eV for Au. 

The threshold energy of carbon atom displacement from CNS lattice in some cases can be considered as independent from the angle 5 (isotropic displacement). The integration of Equation 21.2 for these cases yields for the total displacement cross section the following expression ... 

The calculation of the threshold energy E of carbon atom displacement from the CNS lattice is usually carried out with use of tight-binding molecular-dynamics simulations (Crespi et al. 1996, Krasheninnikov et al. 2005, Zobelli et al. 2007). The total analysis of the collision process in calculations shows that the normal impulse to the lattice atom from the incident electron (8=0) leads... 

The energy loss of the penetrating ions is caused either by electronic interaction with the outer shell electrons or by collisions with the target atoms. If the energy transferred to an atom is above the threshold energy for atomic displacement (>5-50 eV), the atom will be displaced from its initial lattice site. Both the displaced as well as the incident ion can suffer additional collisions with other atoms in the solid, resulting in a collision cascade which causes structural and/or electronic damage. The fact that every ion initiates a different... 

It will be assumed for the moment that the non-bonded atoms will pass each other at the distance Tg (equal to that found in a Westheimer-Mayer calculation) if the carbon-hydrogen oscillator happens to be in its average position and otherwise at the distance r = Vg + where is a mass-sensitive displacement governed by the probability distribution function (1). The potential-energy threshold felt is assumed to have the value E 0) when = 0 and otherwise to be a function E(Xja) which depends on the variation of the non-bonded potential V with... 

When the predicted change in energy and the maximum displacement fall under some threshold, the optimization is completed. 

A wide variety of process-induced defects in Si are passivated by reaction with atomic hydrogen. Examples of process steps in which electrically active defects may be introduced include reactive ion etching (RIE), sputter etching, laser annealing, ion implantation, thermal quenching and any form of irradiation with photons or particles wih energies above the threshold value for atomic displacement. In this section we will discuss the interaction of atomic hydrogen with the various defects introduced by these procedures. 

The origin of the sputtered atoms may result from displacement below the surface of the source, a so-called thermal spike, as well as directly from the surface, depending on the incident energy of the bombarding ions, Et. This must reach a threshold value, E before any atoms are dislodged from the target and... 

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